Infant formulas are commonly used today to provide supplemental or sole source nutrition early in life. These formulas contain protein, carbohydrate, fat, vitamins, minerals, and other nutrients. They are commercially available as powders, ready-to-feed liquids, and liquid concentrates.
Although many infant formulas provide a quality alternative to human milk, they still do not provide the same high level of nutrition as found in human milk. As such, much of the research effort into infant formulas over the past several years has been directed to better understanding the natural constituents of human milk, and then modifying infant formulas accordingly, or at least to the extent possible with currently available technology.
Arachidonic acid and docosahexaenoic acid, for example, have been identified in human milk and subsequently added to synthetic infant formulas. These fatty acids support brain and vision development in infants, and are now commonly found in commercially available formulas such as Similac® Advance® Infant Formula, Isomil® Advance® Infant formula, and Similac® Special Care® Advance® infant formula, all of which are available from Ross Products Division, Abbott Laboratories, Columbus, Ohio, USA.
Lutein has also been identified in human milk. Although it is not currently added to infant formulas as an isolated ingredient, lutein can be found at low concentrations in infant formulas as an inherent ingredient in some of the natural oils commonly used to make such formulas. Lutein is an antioxidant that also happens to concentrate within the retina of the eye. It is generally known that dietary lutein may provide individuals with eye health benefits, and it is speculated that such benefits may be extended to infants receiving lutein from either human milk or supplemented infant formula.
It is now believed that a combination of lutein and docosahexaenoic acid may be particularly important in promoting retinal health and vision development in infants. Both materials are present in human milk and both are known to concentrate in the retina in otherwise healthy subjects. Docosahexaenoic acid (DHA), as a polyunsaturated fatty acid, is highly susceptible to damage by oxidation and degradation within the eye, while lutein is a known antioxidant. It is believed that by adding lutein to infant formulas, not only will it concentrate within the retina, it may also reduce oxidative degradation of the retinal DHA and thus further promote retinal health and vision development in the infant.
It has now been found, however, that lutein concentrations in infant formula must be much higher than the lutein concentrations found in human milk in order to achieve the same plasma lutein concentrations found in breast fed infants due to a lower relative bioavailability of lutein from infant formula. Although infant formulas today typically contain less than about 20 mcg/liter of lutein, most of which comes inherently from added fats and oils, it has now been found that such lutein concentrations must exceed about 50 mcg/liter, preferably from about 100 mcg/liter to about 200 mcg/liter, in order to duplicate plasma lutein concentrations found in exclusively breast fed infants.
Consequently, it has also been found that infant formulas containing combinations of lutein and DHA, as described above, should now be formulated with higher ratios (lutein to DHA) than are commonly found in human milk. These weight ratios of lutein (mcg) to DHA (mg) should now range from about 1:2 to about 10:1.
It has also been found that the severity or risk of retinopathy of prematurity (ROP) is influenced by skin carotenoid levels found in preterm infants fed human milk. This finding suggests that preterm infants can be monitored for skin carotenoid concentrations, and then for those infants demonstrating low skin carotenoid levels, supplemental carotenoids may be administered in amounts sufficient to increase skin carotenoid levels, to thus reduce the risk or severity of retinopathy of prematurity.